Cannot attach QScrollBar to QwtPlot

[mohini]

hello,
Background :
I have Plot a Histogram on QwtPlot using QwtPlotHistogram. then I have been able to magnify the plot in right direction only. Now as I magnify the plot I need A ScrollBar to view the zoomed data. for this I added a QScrollBar.
I am trying to attach a QScrollBar to My QwtPlot .

But I can't connect the QScrollBAr to QwtPlot.

the code which I am trying is : (this is in MyPlot 's constructor)

QScrollBar *hScrollBar = new QScrollBar(Qt::Horizontal,plot->canvas());
connect(hScrollBar,SIGNAL(sliderMoved(double)),thi s->canvas(),SLOT(horizontal_scroll(double)));

horizontal_scroll is my method as :

void MyPlot:: horizontal_scroll(double value)
{
setAxisScale(2, value, value + 105.0);
//plot->setAxisScale(0,50,20);
replot();
}

I am not getting where I am going wrong....!!

Thanx in advance...!

[Uwe]

You also have to write layout code ( moving + resizing the scrollbar ). If you want to have it on top of the plot canvas you have to implement an event filter catching resize and move events for the canvas.

Again look at the ScrollZoomer from the realtime example - it does this.

Uwe

[mohini]

thanx Uwe ..!
But, ScrollZoomer implements QWtPlotZoomer whereas I am using QwtPlotMagnifier ...
Its adding to my confusion ...!!
Can you please elaborate so that I can get it cleared ...!!

[Uwe]

Event filtering is a general Qt feature ( see QObject::installEventFilter() ).

Assuming your plot widget owns your scroll bar, then you have to do something like this:

class YourPlot: public QwtPlot
{
public:
    YourPlot( ... )
    {
         ....
         m_scrollBar = new QScrollBar( Qt::Horizontal, this );
         canvas()->installEventFilter(this);
    }
 
    virtual bool eventFilter(QObject *object, QEvent *e)
    {
        if ( object == canvas() )
        {
            if ( e->type() == QEvent::Move )
            {
                m_scrollBar->move( ... );
            }
            if ( e->type() == QEvent::Resize )
            {
                m_scrollBar->resize( ... );
            }
        }
        return QwtPlot::eventFilter( object, event );
    }
};

class YourPlot: public QwtPlot
{
public:
    YourPlot( ... )
    {
         ....
         m_scrollBar = new QScrollBar( Qt::Horizontal, this );
         canvas()->installEventFilter(this);
    }

    virtual bool eventFilter(QObject *object, QEvent *e)
    {
        if ( object == canvas() )
        {
            if ( e->type() == QEvent::Move )
            {
                m_scrollBar->move( ... );
            }
            if ( e->type() == QEvent::Resize )
            {
                m_scrollBar->resize( ... );
            }
        }
        return QwtPlot::eventFilter( object, event );
    }
};

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But of course you can put your scrollbar also everywhere else independant of the plot canvas geometry.

Uwe